) Chinese Journal ofAstronomy and Astrophysics The Intimate Connection between High and Low Frequency Emission in Blazars

Abstract The author discusses the relationship between X and radiation and radio to op-tical emission in blazars based on recent observations. The availability of densely-sampled light curves at several wavebands for several quasars, BL Lacertae, and two radio galaxies demonstrates that a strong connection exists between high and low frequency emission. The relativistic jet provides the most straightforward explanation of this connection. In the radio galaxies, temporary decreases in the X-ray flux from the central engine precede the appear-ance of bright superluminal knots in the radio jet. The combination of multiwaveband light curves and millimeter-wave imaging with very long baseline interferometry, along with po-larization measurements whenever possible, can map the emission regions and lead to more accurate theoretical descriptions of the physical processes in blazars than has been possible in the past